rtnetlink: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
allocates the maximum size expected for all possible types and adds
sanity-checks at both registration and usage to make sure nothing gets
out of sync. This matches the proposed VLA solution for nfnetlink[2]. The
values chosen here were based on finding assignments for .maxtype and
.slave_maxtype and manually counting the enums:

slave_maxtype (max 33):
	IFLA_BRPORT_MAX     33
	IFLA_BOND_SLAVE_MAX  9

maxtype (max 45):
	IFLA_BOND_MAX       28
	IFLA_BR_MAX         45
	__IFLA_CAIF_HSI_MAX  8
	IFLA_CAIF_MAX        4
	IFLA_CAN_MAX        16
	IFLA_GENEVE_MAX     12
	IFLA_GRE_MAX        25
	IFLA_GTP_MAX         5
	IFLA_HSR_MAX         7
	IFLA_IPOIB_MAX       4
	IFLA_IPTUN_MAX      21
	IFLA_IPVLAN_MAX      3
	IFLA_MACSEC_MAX     15
	IFLA_MACVLAN_MAX     7
	IFLA_PPP_MAX         2
	__IFLA_RMNET_MAX     4
	IFLA_VLAN_MAX        6
	IFLA_VRF_MAX         2
	IFLA_VTI_MAX         7
	IFLA_VXLAN_MAX      28
	VETH_INFO_MAX        2
	VXCAN_INFO_MAX       2

This additionally changes maxtype and slave_maxtype fields to unsigned,
since they're only ever using positive values.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
[2] https://patchwork.kernel.org/patch/10439647/

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index 14b6b3a..0bbaa54 100644 (file)
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -64,7 +64,7 @@ struct rtnl_link_ops {
        size_t                  priv_size;
        void                    (*setup)(struct net_device *dev);
 
-       int                     maxtype;
+       unsigned int            maxtype;
        const struct nla_policy *policy;
        int                     (*validate)(struct nlattr *tb[],
                                            struct nlattr *data[],
@@ -92,7 +92,7 @@ struct rtnl_link_ops {
        unsigned int            (*get_num_tx_queues)(void);
        unsigned int            (*get_num_rx_queues)(void);
 
-       int                     slave_maxtype;
+       unsigned int            slave_maxtype;
        const struct nla_policy *slave_policy;
        int                     (*slave_changelink)(struct net_device *dev,
                                                    struct net_device *slave_dev,

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 8080254..8ca49a0 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -59,6 +59,9 @@
 #include <net/rtnetlink.h>
 #include <net/net_namespace.h>
 
+#define RTNL_MAX_TYPE          48
+#define RTNL_SLAVE_MAX_TYPE    36
+
 struct rtnl_link {
        rtnl_doit_func          doit;
        rtnl_dumpit_func        dumpit;
@@ -389,6 +392,11 @@ int rtnl_link_register(struct rtnl_link_ops *ops)
 {
        int err;
 
+       /* Sanity-check max sizes to avoid stack buffer overflow. */
+       if (WARN_ON(ops->maxtype > RTNL_MAX_TYPE ||
+                   ops->slave_maxtype > RTNL_SLAVE_MAX_TYPE))
+               return -EINVAL;
+
        rtnl_lock();
        err = __rtnl_link_register(ops);
        rtnl_unlock();
@@ -2902,13 +2910,16 @@ replay:
        }
 
        if (1) {
-               struct nlattr *attr[ops ? ops->maxtype + 1 : 1];
-               struct nlattr *slave_attr[m_ops ? m_ops->slave_maxtype + 1 : 1];
+               struct nlattr *attr[RTNL_MAX_TYPE + 1];
+               struct nlattr *slave_attr[RTNL_SLAVE_MAX_TYPE + 1];
                struct nlattr **data = NULL;
                struct nlattr **slave_data = NULL;
                struct net *dest_net, *link_net = NULL;
 
                if (ops) {
+                       if (ops->maxtype > RTNL_MAX_TYPE)
+                               return -EINVAL;
+
                        if (ops->maxtype && linkinfo[IFLA_INFO_DATA]) {
                                err = nla_parse_nested(attr, ops->maxtype,
                                                       linkinfo[IFLA_INFO_DATA],
@@ -2925,6 +2936,9 @@ replay:
                }
 
                if (m_ops) {
+                       if (ops->slave_maxtype > RTNL_SLAVE_MAX_TYPE)
+                               return -EINVAL;
+
                        if (m_ops->slave_maxtype &&
                            linkinfo[IFLA_INFO_SLAVE_DATA]) {
                                err = nla_parse_nested(slave_attr,